Insertion, or coordination, polymerization is a well-known chemical reaction sequence for preparing polymers and copolymers of ethylene, .alpha.-olefins, non-conjugated diolefins and cyclic olefins. In particular, coordination polymerization with Group 4 metallocene catalyst systems is now well-known. Traditional Ziegler monomers, e.g., ethylene and .alpha.-olefins, such as propylene, 1-butene, 1-hexene, and 1-octene, are readily polymerized in the presence of Group 4 transition metals having, as ligands at least one .eta.-5 bound cyclopentadienyl ligand and two univalent anionic ligands where the univalent ligands can be abstracted by an cocatalyst compound so that an activated catalyst compound capable of olefin insertion polymerization is formed.
Geminally disubstituted olefin monomers, such as isobutylene, have been thought to be largely incapable of polymerization by insertion, or coordination, mechanisms. In the chapter on "Insertion Polymerization", Encycl. of Polm. Sci. and Eng., vol. 8, p. 175 (Wiley Interscience, 1988), the statement is made that ". . . 1,1-disubstituted .alpha.-olefins are neither homo- nor copolymerized with other monoolefins." Instead such disubstituted .alpha.-olefins are typically polymerized and copolymerized by cationic or carbocationic polymerization with Lewis acid catalyst systems known to initiate the formation of carbocations. However, since ethylene is not readily polymerized by cationic techniques, see Kennedy, J. P., Carbocationic Polymerization of Olefins: A Critical Inventory, p. 53 et seq. (John Wiley & Sons, 1975), ethylene copolymers with disubstituted .alpha.-olefins are largely unknown.
Despite this prejudice in the art certain ethylene-isobutylene copolymers have been exemplified. Example E of WO 95/29940 describes ethylene/isobutylene copolymerization concurrent with the homopolymerization of both the isobutylene and the ethylene at -20.degree. C. with bis-(cyclopentadienyl)hafnium dimethyl and bis-(pentamethylcyclopentadienyl)zirconium dimethyl, both activated by triphenylmethyl-tetrakis(perfluorophenyl)boron. The amount produced of ethylene-isobutylene copolymer was less than 1.3 weight % of the total polymer products. Copolymerization of 2-methylpropene (isobutylene) and ethylene at 30.degree. C. and 50.degree. C. with ethylene-bis(indenyl)zirconium dichloride when activated with methylalumoxane was reported in "Isotactic Polymerization of Olefins with Homogeneous Zirconium Catalysts", W. Kaminsky, el al, Transition Metals and Organometallics as Catalysts for Olefin Polymerization, page 291, 296 (Springer-Verlag, 1988). Incorporation of isobutylene was reported to be less than 2.8 mol. %, the only example illustrates 1.35 mol. %.
Non-metallocene bis(amido) Group 4 catalyst compounds are also known in the art for .alpha.-olefin polymerization. U.S. Pat. No. 5,318,935 describes bridged and unbridged bisamido transition metal catalyst compounds of Group 4 metals capable of insertion polymerization of .alpha.-olefins. The examples illustrate .alpha.-olefin copolymers and homopolymers of ethylene, propylene, 1-butene, and 1-hexene. U.S. Pat. No. 4,774,301 describes zirconium catalyst compounds corresponding to the formula ZrXR.sub.3 wherein the R groups may include one or more --NR'.sub.2 group, R' being alkyl or aryl of up to 12 carbon atoms. However polymerization capability for vinyl aromatic monomers and highly syndiotactic polymers of them are described and exemplified only with zirconium tetra-n-propoxide for syndiotactic polystyrene. Bridged bis(arylamido) Group 4 compounds proposed for "single site" olefin polymerization are described by D. H. McConville, et al, in Organometallics 1995, 14, 5478-5480. Synthesis methods and compound characterization are presented. Further work appearing in D. H. McConville, et al, Macromolecules 1996, 29, 5241-5243, described the bridged bis(arylamido) Group 4 compounds which upon activation with Lewis acid cocatalysts provided active catalysts for polymerization of 1-hexene. Each of these documents is incorporated by reference for the purposes of U.S. patent practice.
In view of the above, additional means of manufacturing polyolefins incorporating geminally disubstituted olefins is highly desirable. Copolymer compositions comprising .alpha.-olefins and geminally disubstituted olefins, optionally with other polymerizable olefinically-unsaturated monomers, provide new compositions useful in many applications. It also serves the function of economically utilizing the inherent feedstock make-up in petroleum refining processes where fractionation can produce commingled streams of 1-butene and isobutylene.